Applications that exploit the exceptional properties of nanotubes at practical length scales almost invariably raise the fundamental question of nanotube-to-surface contacts. For example, vertically aligned and dense arrays of carbon nanotubes (CNTs) have been demonstrated to be good thermal interface materials, with contact resistances close to some of the best conventional materials elsewhere. Interfacial transport between CNTs and bulk substrates is found to dominate device performance in this application as well as other electrical and thermal applications.